reinstate sw tests

test/client.js

@@ -53,4 +53,28 @@ describe('no real fetch', function () {
 		fetchMock.realFetch = realFetchCache;
 		window.fetch = fetchCache;
 	});
-});
+});
+
+describe('service worker', () => {
+	it('should work within a service worker', () => {
+		return navigator.serviceWorker && navigator.serviceWorker.register('__sw.js')
+			.then(registration => {
+				return new Promise((resolve, reject) => {
+					if (registration.installing) {
+						registration.installing.onstatechange = function () {
+							if (this.state === 'activated') {
+								resolve();
+							}
+						}
+					} else {
+						reject('No idea what happened');
+					}
+				})
+					.then(() => {
+						expect(true).to.be.true;
+						return navigator.serviceWorker.getRegistration()
+							.then(registration => registration ? registration.unregister() : false);
+					})
+			})
+	})
+})